Selective etching and cleaning solutions for dielectric antireflective coatings (DARC), pre-metal contacts comprised of undoped tetraethylorthosilicate (TEOS) and thermal oxides, and doped phospho- and boro-phospho-silicate glasses (PSG & BPSG) and low-k dielectric/copper interconnect structures are important to device design and manufacturing for the most advanced semiconductor technologies. Such process chemicals enable processing advances such as reduction of critical dimension and lower resistivity and capacitance contacts and interconnect.
DARC films, and more generally antireflective coatings (ARC's), are used to minimize undesirable surface layer reflections during photolithography and in so doing provide better pattern definition. DARC films are also employed in Advanced Patterning Technology with amorphous carbon films to extend and enhance existing photolithography to pattern smaller geometry structures. However, it is generally necessary to selectively remove these films after photolithography or plasma etch by either a wet chemical or plasma method.
Both undoped and doped silicon oxides are used as dielectric materials in pre-metal contacts down to doped silicon, polysilicon, and suicides. After plasma etch to open the contact, a contact clean chemistry is applied to selectively remove residues and provide a clean and conductive contact surface while maintaining the contact profile and critical dimension.
Additionally, compositions for removing photoresist and etch residues following plasma etch and ash processes are crucial for optimum electrical performance, reliability, and yield in integrated circuit manufacturing. Back end of line (BEOL) cleaning chemicals need to be capable of cleaning organic, organometallic, and inorganic post etch and post ash residues from copper and aluminum interconnect while not etching the interconnect metal or altering silicon dioxide or low-k dielectrics and their associated materials.
Presently, aqueous and non-aqueous fluoride formulations are used in selective etching and cleaning applications. These compositions are generally comprised of a fluoride component, additives, and a solvent, in many instances water. In selective etch applications, etch rates of many fluoride containing compositions are generally high, requiring very short process times. In addition, the varying stoichiometry of the films to be etched may result in a non-uniform etch that manifests as small islands of film remaining on the substrate surface as depicted in FIG. 1 for the DARC (SixOyNz) selective etchant application. What is needed is an improved etchant composition having improved etch rate, etch selectivity, and etch uniformity criteria on different types of substrates.
Fluoride chemistries, particularly HF/NH4F buffered oxide etch (BOE) and dilute HF, are also widely used for pre-metal contact cleaning. The high silicon oxide etch rates and narrow selectivity properties limit their use in applications where contact CD is below 0.18 μm, aspect ratio is greater than 10:1, and contact architecture uses complex material stacks as depicted in FIGS. 2A & 2B. A fluoride solution that has lower oxide etch rate than BOE or HF, adjustable oxide etch rate selectivity, and good residue removal activity is needed.
Formulations containing various amounts and types of fluoride additives have been used for BEOL cleans particularly when interconnect features are comprised of copper, low-k dielectric and associated materials as depicted in FIG. 3A, and they are also useful for aluminum interconnect systems such as shown in FIG. 3B. Fluoride chemistries are active in dissolving metal oxide and halide residues that are generated from the plasma etch of the interconnect material stack. However, many existing fluoride chemicals will also etch or chemically modify the silicon oxide and low-k dielectrics. This results in undesirable critical dimension enlargement and an increase in dielectric constant.